Compound Interest Calculator
Project savings growth with compound interest.
100% private — runs in your browser, nothing is uploaded.
Future balance
$144,573
Total contributed
$58,000
Interest earned
$86,573
| Year | Balance | Contributed | Interest |
|---|---|---|---|
| 1 | $13,201 | $12,400 | $801 |
| 2 | $16,634 | $14,800 | $1,834 |
| 3 | $20,315 | $17,200 | $3,115 |
| 4 | $24,262 | $19,600 | $4,662 |
| 5 | $28,495 | $22,000 | $6,495 |
| 6 | $33,033 | $24,400 | $8,633 |
| 7 | $37,900 | $26,800 | $11,100 |
| 8 | $43,118 | $29,200 | $13,918 |
| 9 | $48,714 | $31,600 | $17,114 |
| 10 | $54,714 | $34,000 | $20,714 |
| 11 | $61,147 | $36,400 | $24,747 |
| 12 | $68,046 | $38,800 | $29,246 |
| 13 | $75,444 | $41,200 | $34,244 |
| 14 | $83,376 | $43,600 | $39,776 |
| 15 | $91,882 | $46,000 | $45,882 |
| 16 | $101,003 | $48,400 | $52,603 |
| 17 | $110,783 | $50,800 | $59,983 |
| 18 | $121,270 | $53,200 | $68,070 |
| 19 | $132,515 | $55,600 | $76,915 |
| 20 | $144,573 | $58,000 | $86,573 |
Estimates for illustration only. Contributions are assumed to be made monthly. Not financial advice.
How to use the Compound Interest Calculator
- 1Enter your starting amount
Set the initial deposit you're beginning with.
- 2Add a monthly contribution
Set how much you'll add each month (or zero).
- 3Set rate and years
Enter the annual interest rate and how long you'll invest.
- 4Read the projection
See your future balance, interest earned and a year-by-year table.
Examples
| Input | Output |
|---|---|
$10,000, +$200/mo, 7%, 20 yrs | ≈ $145,000 balance |
$1,000, no adds, 5%, 10 yrs | ≈ $1,647 balance |
Free compound interest calculator
This compound interest calculator projects how savings or investments grow over time when interest is reinvested and you keep adding to the pot. Enter a starting amount, an optional monthly contribution, a rate and a time horizon, and see your future balance along with a year-by-year breakdown of contributions versus interest.
Why compounding feels like magic
With simple interest you earn on your principal alone. With compound interest, each period's interest is added to the balance and then earns interest itself. That feedback loop makes the curve bend upward — the growth in the final year of a long investment can dwarf the first year's entirely.
The three levers that matter
The biggest drivers of your final number are time, your contribution rate and the interest rate — in roughly that order for long horizons. Compounding frequency (monthly vs annual) makes only a small difference. Use the year-by-year table to see the moment interest earned overtakes the money you put in. Everything is calculated privately in your browser.
Frequently Asked Questions
What is compound interest?
Compound interest is interest earned on both your original money and on the interest it has already earned. Because each period's interest joins the balance, growth accelerates over time — the effect Einstein reportedly called the eighth wonder of the world.
How is compound interest calculated?
The core formula is A = P(1 + r/n)^(nt), where P is the principal, r the annual rate, n the number of times it compounds per year, and t the years. This calculator also adds your regular contributions period by period.
Does compounding frequency really matter?
It has an effect, but a smaller one than people expect. Monthly versus annual compounding at the same rate differs only slightly. Your rate, how much you contribute, and the number of years matter far more.
How do regular contributions change the result?
Adding a fixed amount every month dramatically increases the final balance, because each contribution starts compounding immediately. Over decades, steady contributions often outweigh the starting deposit.
Why is time the biggest factor?
Compound growth is exponential, so the last few years add far more than the first. Starting earlier — even with smaller amounts — usually beats starting later with more, which is why investing early is so powerful.
Is this financial advice?
No. This is an educational estimate that assumes a constant rate and regular contributions. Real investments fluctuate. The calculation runs privately in your browser.